The conventional cement notation in which C represents CaO, S represents SiO2, A represents Al2O3 and H represents H2O is used in the present document. In this notation, the β-dicalcium silicate belite is, for example, represented by β-C2S since the molar ratio of calcium:silicon (Ca:Si) therein has a value of 2:1, which corresponds to 2[CaO].[SiO2]=Ca2SiO4 in conventional notation.
Belite cements containing dicalcium silicate are known from cement technology and are produced by the conventional process for cement clinker production, however, the production thereof is similarly energy-consuming as the production of portland cement. For this purpose, the raw materials lime and silicon dioxide are milled and mixed in a molar ratio of Ca:Si of about 2. The product is subsequently firstly deacidified at about 800° C. and subsequently fired at about 1250° C. in a rotary tube furnace. The belite clinker formed is milled together with milling additives after cooling.
DE 10 2005 037 771 B4 describes that the deacidified starting materials are milled and blended so as to provide a mixture having a molar ratio of C:S in the range from 1.5:1 to 2.5:1. Any CaO deficit must thereby be compensated by adding quicklime or lime milk. Sealing of the starting material with crystallization nuclei composed of α′L-Ca2 [HSiO4](OH) and subsequent hydrothermal treatment at about 200° C. gives an intermediate containing α-Ca2SiO4(OH)2. After filtration and drying, this intermediate is converted at firing temperatures of from 600° C. to 900° C. into a belite-containing binder and subsequently milled. A disadvantage here is the need for two thermal treatment stages, i.e., a hydrothermal stage and a firing. The product produced by this process is similarly sluggish to react as the material produced in a rotary tube furnace.
DE 10 2009 018 632 B4 describes a starting material containing calcium (Ca), silicon (Si), and oxygen atoms, where 0-50% of the silicon atoms have been replaced by aluminum (Al) atoms, which are present in a molar ratio of C:(S+A), in the determination of which the modal proportions of lime, calcium sulphite and calcium sulphate remain disregarded, of from 1.5:1 to 2.5:1, is firstly produced and admixed with water. The starting material which has been admixed with water in this way is then hydrothermally treated at a temperature of 120-250° C., as a result of which the starting material is converted predominantly into an intermediate. A subsequent reaction milling of the intermediate at a temperature of 100-150° C. in pure form or together with other silicate-containing materials in a mill results in reaction and dewatering to give at least partly the belite-containing binder. A disadvantage here is that calcium carbonate cannot be used directly in this process.